In order to improve the image quality in positron emission tomography (PET), time-of-flight (TOF) PET scanners have been used. For this purpose, detectors with higher timing resolution are required. Timing resolution is expressed as
      Δ    ⁢                  ⁢    τ    ∝            τ              n        Phe            where τ is the decay time of the scintillator, and nPhe is the photoelectron number, which is proportional to light yield. A large photoelectron number or a higher light yield is desired to get better timing resolution.
Computed tomography (CT) has a similar timing issue. For example, fast kV-switching techniques for dual energy CT requires very prompt signals.
To increase light yield, various methods have been used to improve intrinsic properties of scintillation materials. Various methods have also been used to increase light extraction by modifying the light emitting surface of the scintillators. For example, light output from a semiconductor laser and an LED has been improved by roughening the light-emitting surface. For scintillators, a “roughened surface” obtained by lapping the scintillator surface is conventionally used to extract more light from the scintillator. Also, a lithography method has been used to extract more light from scintillation materials by making a photonic crystal structure on the surface of scintillation materials.
Conventionally, optical glue is used to couple the scintillator with the optical sensor (e.g., PMTs and photodiodes). However, optical glue does not have an appropriate refraction index, and therefore, a portion of the light is reflected back into the scintillator due to total reflection. Therefore, the light is not efficiently extracted from the scintillator, which slows the rising of the detected signal pulse, and as a result, deteriorates the timing resolution.
Accordingly, there is a need for an efficient method to improve light extraction from scintillators.